Dual‐Mode Thermal Indicator for Cold‐Chain Logistics Using Multipiezo Li _0.12 Na _0.88 NbO ₃ : Pr ³⁺

Abstract Effective cold‐chain monitoring is crucial for safeguarding vaccine quality and efficacy, particularly under harsh sub‐zero conditions. However, conventional temperature monitoring frequently encounters challenges, including limited operational performance at low temperatures, narrow tracking windows, susceptibility to photobleaching, and poor reproducibility, severely restricting their practical applications. To address these limitations, a dual‐mode thermal indicator capable of both real‐time sensing and recording past temperature changes is developed by integrating fluorescence intensity ratio (FIR)‐based temperature sensing and persistent luminescence‐based time recording, based on Li 0.12 Na 0.88 NbO 3 :Pr 3+ (LNNO:Pr 3+ ). The structure of LNNO:Pr 3+ is located near the morphotropic phase boundary, exhibiting coexisting rhombohedral and orthorhombic phases, which facilitates the creation of a tailored trap state and local structure, enabling dual‐mode optical sensing. The temperature‐dependent FIR between the 1 D 2 → 3 H 4 (610 nm) and 3 P 0 → 3 H 4 (500 nm) energy levels of Pr 3+ ions achieves the highest relative sensitivity (2.18% K −1 ) to date in the range of 103–293 K. Simultaneously, persistent luminescence combined with thermoluminescence enables accurate optical energy storage and time‐temperature recording. Systematic analysis establishes a robust dual‐mode sensing model, demonstrating significant potential for advanced cold‐chain logistics and biomedical storage under low‐temperature conditions.